1. Field of the Invention
The present invention relates generally to the field of machine-knitted garments. More particularly, the present invention is a method for reducing the occurrence of thread loops on the surface of machine-knitted fabric.
2. Background of the Invention
In machine-knitted garments, it is generally desired to cut the threads that would otherwise form loops on the reverse side of a knitted fabric, also called “float threads” or “floats.” Float threads are created when knitting with multiple yarns, particularly when creating patterns with multiple threads in a plurality of colors. The presence of float threads reduces the degree to which a knitted garment can stretch, affecting the fit of the garment. In addition, the experience of donning or wearing a garment may be made uncomfortable as float threads can become caught on the fingers or toes of the person donning the garment.
In the hosiery industry, the lack of stretch in a knitted garment is of particular concern. Specifically for men's socks, the ability of the fabric to stretch adequately can be an issue, as men's sizes must stretch to accommodate men's larger diameter feet and legs. Historically, designers of men's socks have been limited in the range of designs they can attempt by the difficulty in implementing pattern complexity while preserving adequate stretch in the knitted fabric.
To further assist in understanding the problems associated with float threads, FIG. 1 illustrates an example of a knitting pattern 5. In particular, FIG. 1 shows a small segment of a knitted fabric 1 with a plurality of white and black thread loops. The thread loops may be represented in a diagram 2 as white and black squares. The white and black squares form a small portion of a bit-map image 3 and 4, which is a subsection of a graphic image used to represent an entire knitting pattern 5. In this hypothetical example, the knitting pattern 5 is a grid 200 squares wide by 530 squares high, each representing one stitch in the resulting knitted fabric.
FIG. 2 shows a small segment of a knitted fabric in more detail. The first thread 6 is used in the first row of the segment for four loops. A different color of thread 7 is introduced for the fifth and subsequent loops in the first row and the introduction of the thread 7 places a cut end 8 into the knitted fabric. Because the first color of thread 6 is not used again in the row, the knitting machine will eventually cut the thread 9 as it proceeds to knit the remainder of the row.
In the second row of the fabric segment in FIG. 2, a third color 10 has been introduced for the first loop shown. Another color 11 is introduced for the second loop, and continues, creating five loops. The color from the first loop is used again for the seventh loop 12. However, in this row, because the thread 10 was used for too few stitches, the knitting machine was unable to cut the thread, trapping float thread 13 across the reverse of the fabric.
FIG. 3 shows only a float thread, and the loop at either end of the float thread. When a stretching force 14 is applied to the fabric, thread is drawn through each loop 15 in the direction of the stretch. Thread from the far side of the loop 16 is drawn into the loop in response to the stretching force. However, if the thread is relatively inelastic, as is common in natural fibers such as wool or cotton, a float loop 17 is unable to yield to the stretching force, limiting stretch in that segment of the fabric. If a float loop spans more than one loop in a knitted fabric, for example the five loops spanned by float loop 13 in FIG. 2, then the loop extension that could have been contributed by the spanned loops does not occur, limiting the stretch extension of the fabric at the point where the float thread occurs.
In FIG. 4, a highly schematic top view of a typical circular knitting machine is shown, to demonstrate how float threads are created in a fabric. The knitting mechanism consists of a needle circle 18, surrounding a stationary dial cap 19. Below the dial cap is a rotating dial (not visible) to which is fixed an annular saw ring 20 that is toothed about its periphery to provide a series of teeth 21 terminating in cutting edges. Surrounding the needle circle 18 is a latch ring 22. In accordance with the usual practice, the needle cylinder and dial cap are rotated and yarns are placed into and withdrawn from action by the conventional feed, finger and pattern mechanism (not shown) including a computer controller and electronic actuators. Operation of the knitting machine is controlled by the computer in accordance with a pattern programmed by the user. This programmed pattern specifies the operating parameters for the knitting machine, including the yarn feeds to be used in each thread loop for each row of the pattern as discussed above, to result in production of knitted fabric having the desired graphic pattern by the knitting machine.
A cutter mechanism is provided to sever a feed yarn from its source after the end of the yarn has been knitted into the fabric. A typical cutter mechanism includes a flat spring element 23 mounted at one end on a bracket 24 that, in turn, is secured above the rotating saw ring 20. The flat spring element 23 extends circumferentially and at its free extremity terminates in a downturned leg 25 riding on the upper surface of the toothed ring 20. In normal operation, familiar to those conversant in the art of circular knitting, the cutter mechanism cooperates with the toothed ring 20 to sever the yarn engaged over the cutting edges of saw teeth 21.
Continuing with FIG. 4, needle 27 engages an active yarn 26. Subsequent needles miss the yarn 26 until it is reengaged by the needles after needle 28. The angle 29 between needle 27 and needle 28 is small enough that the chord of the knitting circle described by the un-knitted yarn does not pass under the downturned leg 25 of the cutter mechanism and a float thread 30 is created.
In a typical circular knitting machine, the angle 29 and therefore the minimum number of needles that must be skipped to avoid creating float threads are constants. In the example of FIG. 4, eighteen needles must be skipped, one needle more than the distance spanned by thread 30, before a yarn feed is reintroduced, in order for a thread loop to pass under the cutter leg 25, avoiding the creation of a float thread. Any reintroduction of a yarn from a single feed finger before the required minimum number of needles has passed will result in the creation of a float thread in the knitted fabric.
FIG. 5 presents a representation of the graphic pattern 31 for a sock. If a sock is knitted using the pattern, the sock must be turned inside out to see the float threads on the inner surface of the fabric. A visual representation or map of the float threads 32 may be created by representing each float thread as a line of pixels in a drawing, in the same way as in FIG. 1, where sequences of pattern loops 1 are represented by drawing pixel elements in 3 and 4. The map 32 presents the float threads as they will be seen when the sock is turned inside out. It is easier for a designer to understand the specific pattern features that create float threads in a pattern if a float map 33 is presented in the same orientation as the pattern image 31, rather than as seen when the sock is turned inside out. In FIG. 6 through FIG. 10, all float diagrams will be presented in the same orientation as the original pattern.
FIG. 6 is a diagram of a simple sock pattern image 34, a visual map of float threads 35 that would be created if the pattern 34 is knitted, and a histogram chart 37 that provides an indication to a designer or machine operator of where float threads will occur in the knitted sock. The histogram chart 36 has an indicator line 37, labeled with a percentage “45” to indicate that 45% of the stitches in the sock are covered by float threads. In addition, the histogram indicates the percentage of each course of the sock covered by float threads. Three histogram peaks 38 indicate three areas in the sock that will have a majority of the stitches covered with float threads, and consequently the stretch in the sock fabric will be greatly reduced in those areas. Any person skilled in the art will recognize that the methodology for generating the float thread histogram 36 can show numeric stitch percentages or can be used to display more sophisticated measures of stretch reduction, taking into account various factors, such as the length of individual float threads or the stretch characteristics of specific types of yarn.
FIGS. 7-9 present the pattern from FIG. 6, as it may be altered in successive steps by a machine operator or designer in an attempt to reduce float threads in a fabric. Each step of this process requires the operator to create a modified pattern file for the knitting machine, load the file into the machine and knit a physical sock in order to evaluate the success of their pattern modifications. In FIG. 7, the operator may add a second feed for the pattern yarn, represented by a new color 39 in the pattern. The easiest approach, and the one followed by most machine operators and designers, is to replace entire shapes in the pattern with a color from the new yarn feed 39. The average float thread coverage 40 is reduced to 31%, but there are still peaks 41 in the histogram with substantial float coverage. In FIG. 8, the operator introduces a third yarn feed 42 for the pattern color, and sees a reduction in the average float coverage 43 to 27%, with some reduction in the histogram peak 44. In FIG. 9, the operator, having exhausted the easy pattern shapes to replace, has introduced a new yarn feed 45 to replace some areas of the ground color in the pattern. The float thread histogram shows a reduction in float coverage to 10% at 46 with peaks 47. However, at this point many operators will cease their efforts to eliminate floats, as the process has consumed four prototyping passes and considerable time.
The prior art in the field includes a number of other approaches to reducing the number of float threads. For example, U.S. Pat. No. 6,810,696 (Lonati) describes a method for automatically setting up the pattern thread feed units on a circular knitting machine to enable more float thread loops to be cut. The method described begins at the top of a knitted garment, and proceeds row by row to the end of the garment.
However, in a real-world production environment, it is quite possible for a simple automated methodology to require more thread feeds than are available on a specific knitting machine, leaving many threads uncut. In practice, it is very easy to create multicolor patterns requiring more thread feeds than are available on a knitting machine. When prior-art methodologies fail, they may do so in such a way as to leave much of the garment with an untenable number of float threads, and inadequate stretch in the garment fabric. In instances where prior-art methodologies fail to deliver adequate reduction in float threads, practice has shown that there is a need for highly-skilled manufacturing personnel to make decisions to simplify or modify the pattern design, or to collaborate with design staff to make such decisions.
Unfortunately, without adequate means to visualize the end result of the float reduction process and a means to quantify and predict the effects of reduction in uncut float stitches on fabric stretch, staff in both design and manufacturing departments must employ costly trial-and-error repetition of knitting tests in their attempts to correct float problems, an outcome the inventors of the prior methodologies in this field recognized and were explicitly attempting to avoid. Furthermore, in an environment where manufacturing is often conducted at considerable geographical remove from the original designer of a garment, the needed collaboration is at best time-consuming and at worst impossible to achieve, resulting in severe limits being placed on the range of designs considered for production.
Thus, conventional attempts at design optimization by a human operator have the shortcomings of being time-consuming and expensive. In addition, this type of optimization is limited by the skill of the human operator and the limited amount of time and effort that can be devoted to any particular job. Therefore, a need exists for a computer-based method for analyzing and reducing the occurrence of float threads by creating a sorted list of float threads over the entire fabric design, and then assigning available yarn feeds to minimize the creation of float threads in the knitted fabric.